This invention relates generally to radar altimeters, and more specifically to a radar altimeter with forward ranging capability.
The proper navigation of an aircraft in all phases of its flight is based to a large extent upon the ability to determine the terrain over which it is passing, and further based on the ability to determine a position of the aircraft. In this regard, aircraft instrumentation, sensors, radar systems, and specifically, radar altimeters are used in combination with accurate electronic terrain maps. The electronic terrain maps provide the height of objects on the map, and together with the radar altimeter aid in the flight and the planning of a flight path for the aircraft.
As such, radar altimeters are commonly implemented within aircraft. A radar altimeter typically includes a transmitter for applying pulses of electromagnetic energy at regular intervals to an antenna which then radiates the energy, in the form of a transmit beam, towards the earth's surface. A transmit beam from a radar is sometimes said to “illuminate” or “paint” an area which reflects the transmit beam. Based on a configuration of the antenna, the transmit beam includes a main lobe, and one or more side lobes which are separated from the main lobe by an angle.
The radar altimeter further includes a signal receiver which receives return pulses, sometimes referred to as an echo or a return signal. Return pulses are received at an receive antenna, and constitute transmit beams that have been reflected from the earth's surface. It is known that some radar altimeters utilize antennas for both transmitting and receiving. A closed loop servo tracker for measuring the time interval between the transmitted pulse and its associated return pulse also forms a part of the radar altimeter. The time interval between the transmit pulse and the return pulse is directly related to the altitude of the aircraft.
However, problems still exist with controlled flights into certain terrain. For example, aircraft are sometimes required to fly at very low altitudes. Flying at low altitude increases the probability that certain terrain features are in front of the aircraft, in the flight path, rather than safely below the aircraft, as is the case at normal flight altitudes.
Known radar altimeters utilized in aircraft are generally incapable of detecting objects that are in a flight path. Examples of such objects include, for example, tall buildings, or the side of a cliff. While an aircraft equipped with a radar altimeter can determine an altitude, the aircraft is not able to recognize objects in front of it if not equipped with, for example, a costly scanning laser radar. Problems also exist even when the scanning laser radar is implemented within an aircraft since they are sometimes rendered ineffective when encountering one or more of rain, fog, and smoke.